Mitochondrial genome plasticity among species of the nematode genus Meloidogyne (Nematoda: Tylenchina)

Abstract

The mitochondrial (mt) genomes of the plant-parasitic root-knot nematodes Meloidogyne arenaria, Meloidogyne enterolobii and Meloidogyne javanica were sequenced and compared with those of three other root-knot nematode species in order to explore the mt genome plasticity within Meloidogyne. The mt genomes of M. arenaria, M. enterolobii and M. javanica are circular, with an estimated size of 18.8, 18.9 and 19.6 kb, respectively. Compared to other nematodes these mt genomes are larger, due to the presence of large non-coding regions. The mt genome architecture within the genus Meloidogyne varied in the position of trn genes and in the position, length and nucleotide composition of non-coding regions. These variations were observed independent of the species' natural environments or reproductive modes. M. enterolobii showed three main non-coding regions whereas Meloidogyne chitwoodi, Meloidogyne incognita, M. javanica and M. arenaria had two non-coding regions, and Meloidogyne graminicola had a unique large non-coding region interrupted by two trn genes. trn genes were positioned in different regions of the mt genomes in M. chitwoodi, M. enterolobii and M. graminicola, whereas the trn gene order was identical between M. arenaria, M. incognita and M. javanica. Importantly, M. graminicola had extra copies of trnV and trnS2. High divergence levels between the two copies of each trn might indicate duplication events followed by random loss and mutations in the anticodon. Tree-based methods based on amino acid sequences of 12 mt protein-coding genes support the monophyly for the tropical and mitotic parthenogenetic species, M. arenaria, M. enterolobii, M. incognita and M. javanica and for a clade that includes the meiotic parthenogenetic species, M. chitwoodi and M. graminicola. A comparison of the mt genome architecture in plant-parasitic nematodes and phylogenetic analyses support that Pratylenchus is the most recent ancestor of root-knot nematodes.

Keywords: Duplication; Mitochondrial genome architecture; Root-knot nematode; trn genes.